Major review confirms link between chemical in plastics and obesity symptoms

Early-life exposure to a chemical commonly used to make plastics in food packaging is connected to the development of obesity-related symptoms in rodents, the first major review of existing research suggests.

While energy imbalance (more calories being consumed than worked off by the body) is considered the main cause of obesity, a growing body of evidence suggests that other risk factors, such as exposure to endocrine-disrupting chemicals, also contributes.

In particular, early-life exposure to obesogens – the chemicals that alter the hormonal pathways which regulate lipid metabolism – may result in a higher susceptibility to developing obesity.

Researchers from Brunel University London, New York University and Vrije Universiteit Amsterdam conducted a review and meta-analysis of prior studies on the connection between these hormone-disrupting chemicals and obesity in rats and mice to determine whether a link exists.

The review explored 61 papers related to research on the connection between bisphenol A (BPA) and obesity-related measurements, including body weight, fat weight, and circulating or tissue levels of triglycerides, leptin and free fatty acids.

The researchers conclude that exposure to BPA during development is positively associated with obesity-related outcomes later in life, including fat weight, triglyceride levels, and free fatty acid levels.

There were stronger positive associations between BPA exposure and obesity-related outcomes in male rodents than in females, as well as stronger positive associations at doses below the current recommended daily exposure limit used in the USA.

However, while there was a significant association between low level exposures to BPA early in life and rodents accumulating more fat (increased adiposity and circulating lipid levels), there was a negative association found between exposure and overall body weight. The authors reflect that this may be due to the large numbers of studies that reported body weight when testing BPA at high doses. These high doses are likely to be toxic to the developing animal, resulting in overall weight loss.

BPA is mainly used in manufacturing plastics and resins used in the production of food packaging and coatings. It can leach into food and has been detected in 93% of urine samples tested in the US, as well as in amniotic fluid, neonatal blood, placenta, cord blood and human breast milk.

To the research team’s knowledge, only a limited number of animal studies examining the effect BPA has on hormones or metabolism was taken into account when government guidelines for the daily tolerable BPA exposure for humans were set. They are now calling for authorities to re-consider these levels set for safe exposure.

Review senior author and Professor of Toxicology at Brunel, Juliette Legler, explains: “Our study concludes that BPA is associated with several obesity-related outcomes in rodents when doses are at the same level, or often below, the current reference dose for BPA in the United States. In Europe, tolerable dose levels have been set by the European Food Safety Authority mainly based on the adverse effects BPA exposure has on the kidneys of mice rather than obesity-related outcomes.

“While our findings are subject to a number of limitations and should be interpreted with caution, we believe they support the need to re-examine BPA safety levels for the human population.

“This is further supported by the fact that BPA has recently been identified as an endocrine-disrupting chemical within Europe based on adverse interactions of BPA with reproductive function, mammary gland development, cognitive function and metabolism. Two human studies in Spain and New York also recently reported associations between prenatal BPA exposure, measured in mothers’ urine, and obesity-related outcomes.

“It’s important to note that although this review focused on BPA studies, other chemicals have also been identified as potential obesogenic chemicals, including several pesticides, brominated flame retardants, and phthalates, which are used in everything from food packaging to cosmetics to cleaning products.”